Category Archives: How To

In previous articles, I’ve described how to test System.out with JUnit and how to test log4j with JUnit. This article describes how to test log4j2 logging with JUnit. This largely follows the same technique as testing log4j logging but using the the newer log4j2 APIs. Differences between log4j and log4j2 log4j2 follows a similar design read more »

Following a recent article on how to Test System.out with JUnit, here’s a follow up on how to test log4J with JUnit. This article describes a technique to test log4J output in a JUnit test by adding a custom appender. This allows us to verify that log4j output contains expected Strings.

JSPs compile to Java code at run time. This is helpful if we want to test code changes without a build and deploy. However, if errors are introduced, they may not be spotted till it’s too late. A useful compromise is to validate JSPs at build time to verify that they will compile. The validator catches syntax errors before the application deploys and starts. This speeds up our build and test cycle and prevents silly mistakes slipping through to production code.

Thymeleaf is a popular templating engine, particularly with Spring projects. Spring Boot has chosen Thymeleaf as the view technology of choice, largely replacing the need for JSP. With old JSPs, custom tag libraries provided integration with various technologies, including Spring Security. A similar library exists to integrate Thymeleaf and Spring Security – the Thymeleaf Spring read more »

It can be useful to verify output to System.out in a unit test. For example, if you’re testing application logging or if you’re using log output to sense some other behaviour. It can be tricky to properly mock behaviour of System.out but fortunately, it is possible to test System.out using JUnit.

Spring Boot Actuator provides assistance for application monitoring. Out of the box it provides information on application health, configuration and logging. It’s trivial to enable: simply add the spring-boot-starter-actuator dependency to a Spring Boot project in Maven or Gradle and it just works! The monitoring information is provided as JSON from HTTP endpoints or via JMX.

The Spring Boot Actuator trace endpoint is particularly handy. By default it shows the last 100 HTTP requests made to the application. This article walks through an Actuator demo and shows some of the configuration options to get the best from this feature.

The wonderful docker-maven-plugin from Spotify is a great way to build Docker images from Maven. If you bind it to Maven phases, it can be used to make a one-step build of a project artifact and its Docker image. For example, if you bind the Docker Maven plugin’s build goal to the Maven package phase, read more »

A standard use case for Docker is to build a container to run a pre-built application so that the containerized app can be run on any Docker enabled host. The application and the container are sometimes developed and built separately. First the application is built, then a container is defined and built to include the application. However, it can be better to promote the Docker container to a first-class build artifact. That is, the build process always builds the deployed component and its container at the same time. This saves a manual build step and also ensures that the Docker container is always up to date with the latest application build. It allows us to easily develop and test against the Dockerized application directly – every build results in a new deployable container.

There are a number of ways to do this. This article looks at hooking the Docker tasks into the Maven build process.